This invention relates to an image forming apparatus and a method of image formation which make use of a light-accepting sheet coated with microcapsules encapsulating a colorless dye and a photopolymerizing agent and an image receiving sheet coated with a developer material and forms a color image on the image receiving sheet through exposure and compression processes.
Japanese Patent Publication Tokkai 58-88739 has disclosed a method of forming through exposure to light a selectively hardened image on a light-accepting sheet coated with microcapsules encapsulating a colorless dye and a photopolymerizing agent (such as photopolymerizing monomers) and compressing it together with an image receiving sheet coated with a developer material having a chromogenic effect on the dye to thereby form a color image on this image receiving sheet. When an image of an original document is projected on such a light-accepting sheet, microcapsules at areas exposed to light are hardened and a selectively hardened image is formed on the sheet. If an image receiving sheet coated with a developer matter is placed on top of this light-accepting sheet and pressed together therewith, microcapsules which have not been hardened are ruptured and the colorless dye encapsulated therein flows out and reacts chromogneically with the developer material on the image receiving sheet, forming a color image thereon. In summary, copies of an image from an original document can be obtained by a copier of a different kind provided with separate supply sections for light-accepting and image receiving sheets and merely by supplying sheets from these supply sections and carrying out exposure and compression processes. Since light-accepting sheets are coated with microcapsules which are weak against externally applied forces, however, the paper transporting system of such a copier must be carefully designed such that no external force will be applied on the microcapsules. Although cassettes are frequently used in devices for supplying sheets of paper, a paper supplying cassette requires a feeder roller which comes into contact with the sheet surface. Thus, cassettes are not preferable for use with light-accepting sheets coated with microcapsules.
In view of the above, it has been proposed to provide light-accepting sheets in the form of a roll and to wrap it around one of a pair of compression rollers such that they can be supplied without requiring the help of a paper feeder roller and that the rotary motion of the compression rollers themselves serves to supply them. With a copier thus structured, however, the so-called exposure point where light exposure takes place and the compression point where the compression rollers apply pressure are separated on the compression rollers. At the end of an image forming process, the wrapped roll of light-accepting sheets has already passed the exposure point by the same distance as that between the exposure and compression points. When the next image forming process is started, therefore, the part of the light-accepting sheet corresponding to this length cannot serve to form any image and is wasted.
Another problem with a copier of this type is that, since the compression rollers are usually set to apply a fairly large pressure therebetween when the light-accepting and image receiving sheets are compressed together, the light-accepting sheet which is constantly subjected to such a large pressure at the pressure point tends to become or to move along a zig-zag trajectory as it is transported thereby.